1. Field of the Invention
The present invention relates to a head-up display device, and more particularly to a head-up display device which utilizes a beam combiner having a diffraction grating such as a hologram and which superimposes scenery in front of the device on an image generated by an image generator to allow observation thereof in one view field. A beam combiner of the present device may be mounted on a front glass of a car or aeroplane so that the image generated by the image generator such as a CRT or two-dimension LED array is displayed to an observer at a driver seat through the beam combiner.
2. Related Background Art
A display device of this type is disclosed in U.S. Pat. No. 4,218,111. In this type of device, it is also required to correct an aberration created by the diffraction grating of the beam combiner in order to clearly display the image. In the aberration correction, a chromatic aberration is an important factor where a band width of the light from the image generator is relatively wide.
In the past, in order to correct such an aberration created by the beam combiner, a relay optical system is arranged between the beam combiner and the image generator. However, even if the beam combiner is mounted on the front glass of the car facing the driver and the image generator and the relay optical system are arranged, it is not easy to correct the aberration for a periphery (off-axis) of the image, because the front glass curves laterally and the shape thereof is not laterally symmetric about a center axis of the car while the driver sits on the left or right side of the center axis and hence the front glass and the beam combiner laterally incline with respect to the relay optical system.